This invention relates to a process for forming an azomethine compound, comprising reacting a compound having an active methylene group or methine group with an arylprimaryamine compound in the presence of a base and an oxidizing agent and in a solvent medium containing a ketone compound having C1-C4 alkyl groups at a temperature low enough to provide a yield of the azomethine product of at least 50 mole %.
Chemical production ideally requires a process which offers high yield with minimal impact on the environment. These factors, along with careful choice of reagents, can lead to a low cost production process. The most widely used method for producing azomethine compounds consists of the oxidative condensation of an activated methylene or methine group containing compound xe2x80x9cAxe2x80x9d with an arylprimaryamine compound xe2x80x9cBxe2x80x9d in the presence of a base. Both one-phase and two-phase systems have been used.
One-phase systems typically require an organic solvent which adequately solubilizes the organic reactants. Examples which have been used are ethyl acetate, methylene chloride, and methanol. U.S. Pat. No. 5,122,611 describes a method for producing an azomethine dye which comprises oxidatively condensing an active methylene- or methine-containing compound, except those containing a sulfonic or carboxylic acid group, and p-phenylenediamine, except those containing a sulfonic or carboxylic acid group, in the presence of methylene chloride as a solvent under a basic condition. However, the organic reactants can require a large volume of such solvents to be adequately soluble. Lower molecular weight ketones such as acetone, would be thought to be a good choice for a solvent, as it typically has good solubility of the organic reactants and is also environmentally benign. However, these ketones appear to adversely affect the yields, presumably as a result of an unwanted side reaction. Therefore, ketones tend to be regarded as a problem as opposed to a potential solvent for such a reaction.
Two-phase systems (i.e. an organic and an aqueous phase) require that the organic solvent is not water miscible, which therefore limits the solvent choice to those such as methylene chloride (dichloromethane), ethyl acetate, toluene, heptane, propyl acetate, etc. However, to ensure adequate conversion to product, only more polar solvents such as methylene chloride or ethyl acetate can be used. The solvent of choice would be dichloromethane, but this solvent has strong environmental reasons for avoiding its use. Simple N-alkyl acetates would potentially be a good choice as solvent, but do not typically give such good separation of the organic phase from the aqueous phase, resulting in production problems. Also, in two-phase systems, the water phase adds considerable volume to the reaction, reducing productivity and requiring additional process steps for its removal.
It is a problem to be solved to provide a process for preparing an azomethine compound in good yield without significant environmental complications.
The invention provides a process for forming an azomethine compound, comprising:
(a) reacting a compound xe2x80x9cAxe2x80x9d having an active methylene group or methine group with an arylprimaryamine compound xe2x80x9cBxe2x80x9d;
(b) in the presence of a base and an oxidizing agent and in a solvent medium containing a ketone compound having the formula R1C(O)R2 wherein R1 and R2 are independently C1-C4 alkyl groups;
(c) at a temperature low enough to provide a yield of the azomethine product of at least 50 mole % based on compound A.
The process provides good yield without creating environmental concerns associated with other solvent materials such as methanol and methylene chloride.
The invention is generally described above. Compound A contains an active methylene (xe2x80x94CH2xe2x80x94) group or methine (xe2x80x94CH less than ) group. Such compounds include, for example, those with an acylacetamide group such as a xcex2-keto carboxamide group. Specific examples are an acyl acetanilide such as a benzoylacetanilide or a pivaloylacetanilide. These compounds are useful yellow dye-forming couplers in the photographic arena. The methine group may be substituted with an non carbon group such as a halogen, nitrogen, oxygen or sulfur linked group. Compound B is an arylprimaryamine. Typical of such compounds are 1xc2x0 amine developing agents such as a phenylene diamine especially a paraphenylenediamine. As indicated hereinafter, these compounds may be substituted.
The reaction requires the co-presence of a base and an oxidizing agent and in a solvent medium containing a carbonyl compound having the formula R1C(O)R2 wherein R1 and R2 are independently C1-C4 alkyl groups. The base may be any basic material that provides a pH value in the desired range, typically 7 to 13.5. Most useful are the inorganic bases such as the carbonates, bicarbonates, and phosphates. Potassium carbonate is conveniently employed. Any oxidizing agent is suitably employed such as a persulfate. Ammonium persulfate is useful for this purpose. Although the amount of oxidizing agent may vary with the acylacetamide selected, suitable amounts are 0.9 to 4.0 equivalents to Compound A with 0.9-2.1 and 1.9-2.1 being typical. The ketone component is one with relatively short alkyl substituents, ranging up to 4 carbon atoms. Butanone and acetone are readily used with acetone (dimethylketone) being the most useful.
The reaction is carried out at a controlled temperature so that the yield is at least 50 mole % based on compound A. It has been found that temperatures above 25xc2x0 C. cannot be expected to satisfy this requirement. In a preferred mode the temperature is less than 20xc2x0 C. and more desirable form 4-12xc2x0 C. With homologous ketones, slight variations in these temperature ranges can be expected.
The relative equivalents of Compound A to Compound B suitably range form 0.9 to 1.5 and more typically 0.9 to 1.1. The amount of base depends on the specific base and the specific type of acylacetamide employed and typically ranges from 2 (for a dibasic compound) to 30 per mole of compound A, with 4-6 typically employed. The reaction time is dependent on the rate of addition of oxidizing agent and is typically 0.5 to 12 hours with 1-8 and more usually, 2-6 hours being employed.
Typical examples of dyes that are conveniently made using the process of the invention have the following general formula I. 
wherein
A is chloro, C1-C4 alkoxy such as methoxy or isopropoxy, methyl or trifluoromethyl;
B is H;
C is H or chloro;
D is H, chloro, carboxyl, sulfonamido, carbonamido, alkoxy, sulfamoyl or sulfonyl;
R is a substituent such as an alkyl group, especially tertiary or methylcyclopropyl, or an aryl group such as a phenyl group; and
Ar is suitably a group having the formula: 
where X is H, or a methyl, methoxy or carbonamido group; and each Y and Z are H or an independently selected substituent group; provided that Y and Z may join to form a ring. Ar may also be 